Hydrogen storage material, method for producing the same, hydrogen storage tank, hydrogen storage system, and fuel cell vehicle

ABSTRACT

A hydrogen storage material of the present invention comprises a plurality of planar molecular layers stacked, and a particle being inserted into the planar molecular layers to define an interlayer distance between the planar molecular layers. Because the hydrogen storage material of the present invention has a sufficient hydrogen storage capacity, it is possible to realize a fuel cell vehicle capable of storing a sufficient amount of hydrogen to attain a long-distance drive.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a hydrogen storage material, ahydrogen storage tank, a hydrogen storage system, a fuel cell vehicle,and a method for producing the hydrogen storage material.

[0003] 2. Description of the Related Art

[0004] Recently, to overcome growing global environment issues, hydrogenhas received attention as a clean energy source. With this tendency, thedevelopment of technologies for producing, storing and applying hydrogenhas been accelerated. In a hydrogen storage system using a hydrogenstorage material, it is presently considered that a hydrogen storagealloy is the most practical hydrogen storage material. In the best-knownLaNi5-based hydrogen storage alloy, the hydrogen storage ratio is 1.4%by weight at normal temperature and at a hydrogen pressure of 1 MPa.Even in a vanadium-based hydrogen storage alloy, which recently hasattracted attention, the hydrogen storage ratio is 2.4% by weight.Because of these facts, it is considered that the hydrogen storagecapacity has not yet reached a practical level. As another hydrogenstorage material, a carbon-based material containing carbon as a basematerial, such as graphite, activate charcoal, or carbon nano-tubes isknown. However, graphite shows a hydrogen storage capacity only in rarecases. The hydrogen storage ratio of activate charcoal is less than 1%by weight and that of carbon nano-tubes is considered to be 3% by weightor less.

[0005] Assuming that a hydrogen storage tank containing a hydrogenstorage material is used in a fuel cell vehicle, in order to attain adesired 500 km-cruising distance on a single charge of hydrogen, about5-kg hydrogen storage capacity would be required. However, none of theaforementioned hydrogen storage materials can satisfy this requirement.This may be because each of the hydrogen storage materials does not havea molecular structure suitable for storing hydrogen. For example, planarmolecular layers of graphite, namely, graphenes, have an interlayerdistance of about 0.34 nm, which is too narrow to store hydrogen.Accordingly, in order to store hydrogen, the interlayer distance ofgraphenes must be increased. As a structure to trap gas in theinterlayer space of a planar layer structure, a planar structure formedof a mixture of small planar molecules is known (see Japanese PatentApplication Laid-Open No. 2000-24495).

SUMMARY OF THE INVENTION

[0006] In the structure formed of a mixture of small planar molecules,the space between the parallel layers of the structure which isconsidered to store hydrogen in a largest amount is restricted by thesize of the molecules used therein. As a result, it is not easy toattain a high hydrogen storage capacity. On the other hand, as is shownin the aforementioned patent publication, when planar molecules such asgraphite and spherical molecules are alternately stacked to form aparallel layered structure, individual layers must be stacked one byone, so that such a manufacturing process is not practical. In thiscase, since the space between the graphite layers itself is not used forstoring hydrogen, the storage amount per volume or weight is not high.Also, in the case where fullerene is used as the spherical molecule,since fullerene is more easily hydrogenated than planar-form carbon, itis hydrogenated during the storage of hydrogen. As a result, this casehas problems in that the recovery amount of hydrogen decreases and thespace for storing hydrogen is decreased.

[0007] The present invention was made in consideration of theabove-described problems. It is an object of the present invention toprovide a hydrogen storage material having a sufficient hydrogen storagecapacity, a hydrogen storage tank, a hydrogen storage system, a fuelcell vehicle and a method for producing the hydrogen storage material.

[0008] The first aspect of the present invention provides a hydrogenstorage material comprising: a plurality of planar molecular layersstacked; and a particle being inserted into the planar molecular layersto define an interlayer distance between the planar molecular layers.

[0009] The second aspect of the present invention provides a method forproducing a hydrogen storage material comprising: arranging a planarmolecular layer material and a metal material at different places in avacuum chamber, followed by sealing the chamber; and controlling thetemperatures of the planar molecular layer material and the metalmaterial, independently, to insert a metal atom constituting the metalmaterial into planar molecular layers formed of the planar molecularlayer material.

[0010] The third aspect of the present invention provides a hydrogenstorage tank, comprising: a hydrogen storage material including aplurality of planar molecular layers stacked, and a particle beinginserted into the planar molecular layers to define an interlayerdistance between the planar molecular layers.

[0011] The fourth aspect of the present invention provides a hydrogenstorage system, comprising: a hydrogen storage tank including a hydrogenstorage material which has a plurality of planar molecular layersstacked, and a particle being inserted into the planar molecular layersto define an interlayer distance between the planar molecular layers.

[0012] The fifth aspect of the present invention provides a fuel cellvehicle, comprising: a hydrogen storage system comprising a hydrogenstorage tank including a hydrogen storage material which has a pluralityof planar molecular layers stacked, and a particle being inserted intothe planar molecular layers to define an interlayer distance between theplanar molecular layers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The invention will now be described with reference to theaccompanying drawings wherein;

[0014]FIG. 1 is a schematic view showing a structure of a hydrogenstorage material according to the present invention;

[0015]FIG. 2 is a schematic view showing a method for producing thehydrogen storage material according to the present invention;

[0016]FIG. 3 is a graph showing the calculated hydrogen storage amount(by weight %) of a hydrogen storage material in Example 1 and theComparative Example;

[0017]FIG. 4 is a graph showing the calculated hydrogen storage amount(by volume %) of a hydrogen storage material in the Example 1 and theComparative Example;

[0018]FIG. 5 is a graph showing the calculated hydrogen storage amount(by weight %) of a hydrogen storage material in Example 2 and theComparative Example;

[0019]FIG. 6 is a graph showing the calculated hydrogen storage amount(by volume %) of a hydrogen storage material in the Example 2 and theComparative Example;

[0020]FIG. 7 is a cross-sectional view showing a hydrogen storage tankfilled with a hydrogen storage material according to the presentinvention;

[0021]FIG. 8 is a schematic view showing a hydrogen storage system usinga hydrogen storage tank according to the present invention; and

[0022]FIG. 9 is a schematic view showing a fuel cell vehicle using ahydrogen storage system according to the present invention.

DETAILED DESCRIPTIONS OF THE PREFERRED EMBODIMENT

[0023] A hydrogen storage material, a method for producing the hydrogenstorage material, a hydrogen storage tank, a hydrogen storage system,and a fuel cell vehicle according to the present invention will now beexplained in detail with reference to the embodiments shown in thedrawings.

Hydrogen Storage Material

[0024] As shown in FIG. 1, a hydrogen storage material according to thepresent invention includes a plurality of stacked planar molecularlayers 1 and particles 2, which are inserted between the molecularlayers 1 and increase the interlayer distance between the planermolecular layers 1. The particles 2 are chemically bound to the layerswhile being inserted between the molecular layers 1.

[0025] The planar molecular layer 1 is primarily formed of carbon suchas graphene constituting graphite. Note that it is possible for theplanar molecular layer 1 to contain a metal element in the molecule. Themetal element may be selected from scandium (Sc), titanium (Ti),vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co),nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), aluminium (Al),potassium (K), rubidium (Rb), and cesium (Cs).

[0026] The particle 2 is selected from alkaline metal atoms such aspotassium, rubidium, and cesium. By inserting such a particle 2 betweenplanar molecular layers 1, the interlayer distance between graphitelayers increases, so that hydrogen can be stored in the interlayer spacebetween the graphite layers.

Method for Producing Hydrogen Storage Material EXAMPLE 1

[0027] In this example, an alkaline metal element is inserted betweengraphene layers by a vapor reaction method. This method is performed inaccordance with the following steps i) and ii).

[0028] i) As shown in FIG. 2, arranging an alkaline metal and graphiteas a planar molecular layer material at different places in a vacuumchamber, namely, a glass tube 3, followed by sealing the tube.

[0029] ii) Controlling the temperatures of the alkaline metal andgraphite, independently, to insert the alkaline metal into graphite.When potassium is used as an alkaline metal, gaseous potassium isbrought into contact with graphite, by increasing the temperature ofgraphite to 500° C. or more and controlling the difference intemperature between potassium and graphite at 150° C. or more, therebycausing an insertion reaction to produce a hydrogen storage materialhaving a potassium as an interlayer compound.

[0030] By placing the hydrogen storage material thus produced inhydrogen gas under pressure of about 5 to 10 MPa, the hydrogen storagematerial stores hydrogen into the interlayers thereof.

[0031] Note that the interlayer distance of the hydrogen storagematerial is measured usually by X-ray diffraction (XRD) or transmissionelectron microscopy (TEM). The interlayer distance of the graphitelayers having an alkaline metal element (potassium) inserted therein andfurther storing hydrogen therein was about 0.85 nm, as measured by XRD.

[0032] Also, when a compound having cesium (Cs) serving as an alkalinemetal between layers was formed in the same manner, the interlayerdistance of graphite layers having hydrogen stored therein was about0.81 nm. Note that an element and a compound other than an alkalinemetal may be inserted.

[0033] When no hydrogen is stored to graphite having alkaline metalatoms inserted therein, the interlayer distance is about 0.5 to 0.6 nm.This is because, the alkaline metal atoms form a single layer betweengraphite layers, as shown in FIG. 1. In other words, this is because aunit of graphene-alkaline metal atom-graphene is repeated to form agraphite intercalation compound.

[0034] However, when hydrogen is inserted between graphite layers,alkaline metal atoms form a plurality of layers between the graphitelayers. More specifically, a plurality of alkaline metal atoms arearranged, for example, graphene-alkaline metal atom-alkaline metalatom-graphene, in the direction perpendicular to the planar direction ofgraphene. As a result, the interlayer distance can exceed 0.8 nm.

[0035] The calculation results of hydrogen storage amounts according tothe Example 1 will be shown below. This calculation was based on theMonte Carlo method. This is a probabilistic method using a random numberfor arranging molecules under a probabilistic rule and is frequentlyused for simulation of a system under a thermodynamic equivalent state.In this embodiment, the calculation was made assuming that theintermolecular force (potential) between carbon atoms, that is, asecondary six-membered ring of carbons (graphene), and a hydrogenmolecule, was 2.9 kJ/mol in agreement with experimental results.

[0036]FIG. 3 is a graph showing the hydrogen storage amount (% byweight) versus the interlayer distance of graphite at a temperature of20° C. and a pressure of 10 MPa. In FIG. 3, the point indicated by thearrow A shows the calculated interlayer distance of graphite only, andit was found that hydrogen is not stored at all. In FIG. 3, a regionenclosed by an oval figure indicated by the arrow B shows the calculatedhydrogen storage amounts with respect to the structure corresponding tothe Example 1. From the figure, it is found that the hydrogen storagecapacity is exhibited after the interlayer distance increases andreaches 0.8 nm. The hydrogen storage capacity (% by weight) furtherincreases up to about 6% by weight with an increase of the interlayerdistance, however, the storage amount per unit volume decreases as shownin FIG. 4. The carbonaceous hydrogen storage material has a smallspecific weight. Because of this, when a structural element containingthe hydrogen storage material is arranged in a limited space such as avehicle, the storage amount per unit volume also becomes an importantfactor for evaluating its storage capacity. In consideration of thesefactors, the most suitable interlayer distance becomes 0.8 to 1.2 nm inthis embodiment.

EXAMPLE 2

[0037] When a foreign element is inserted into graphene of graphite, thenumber of electrons within graphene changes, increasing theabsorbability. In the Example 2, a metal element was inserted as theforeign element into graphene in addition to the constitution of theExample 1, thereby increasing the potential between hydrogen andgraphene to 5 kJ/mol, which is about 1.7 times as high as that of theExample 1. The amount (obtained through calculation) of hydrogen storedby the hydrogen storage material according to this example is shown inFIGS. 5 and 6. More specifically, FIG. 5 is a graph showing the hydrogenstorage amount in terms of % by weight, indicating that hydrogen isstored at an interlayer distance of 0.8 nm or more, in the same as inthe Example 1. When the interlayer distance reaches 1.2 nm or more, thestorage amount per volume decreases. From these facts, the most suitableinterlayer distance in the Example 2 is 0.8 to 1.2 nm, and morepreferably, 1.0 to 1.2 nm.

COMPARATIVE EXAMPLE

[0038] The point indicated by the arrow A in FIGS. 3 to 6 shows theamount (obtained through calculation) of hydrogen stored by a generalgraphite. As is apparent from the figure, hydrogen is not absorbed atall.

[0039] As is explained in the Examples 1 and 2, and the ComparativeExample, the structure formed of graphite constituting a plurality ofplanar molecular layers (graphenes) and an alkaline metal insertedbetween planar molecular layers makes it possible to realize a highlystable hydrogen storage material having a sufficient hydrogen storagespace and to be used suitably in a vehicle.

[0040] In the Examples 1 and 2 mentioned above, the particle to beinserted in planar molecular layers is an alkaline metal atom, however,an alkaline metal molecule may be inserted.

[0041] It is particularly preferable that the particle be chemicallybound to a planar molecular layer (graphene in the Examples 1 and 2). Itis also preferable that the planar molecular layer be formed primarilyof carbon.

[0042] Furthermore, as is apparent from FIGS. 3 to 6, the interlayerdistance between the planer molecular layers having hydrogen storedtherein is preferably 0.8 to 1.2 nm.

[0043] Furthermore, it is preferable that the alkaline metal atomserving as a particle insert be at least one of potassium, rubidium, andcesium.

[0044] In the Example 2 mentioned above, a foreign element,particularly, a metal element, is inserted into graphene, therebyincreasing the potential between hydrogen and graphene to 5 kJ/mol,which is about 1.7 times as high as that of the Example 1. From this, itis preferable that a metal element be contained in a molecule of theplanar molecular layer. The metal element is preferably any one ofscandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese(Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn),gallium (Ga), aluminium (Al), potassium (K), rubidium (Rb), and cesium(Cs).

[0045] A method for producing a hydrogen storage material includes stepsof arranging a planar molecular layer material and an alkaline metalmaterial at different places in a vacuum chamber such as a glass tube,followed by sealing the chamber; and controlling the temperatures of theplanar molecular layer material and the alkaline metal material,independently, to insert a metal atom constituting the alkaline metalmaterial into the planar molecular layers formed of the planar molecularlayer material. By virtue of the process, it is possible to easily andreliably produce a highly stable hydrogen storage material having alarge hydrogen storage capacity per unit volume or unit weight.

Hydrogen Storage Tank

[0046] An embodiment of a hydrogen storage tank having a hydrogenstorage material according to the present invention placed therein willbe explained with reference to FIG. 7.

[0047] In the hydrogen storage tank 10 according to this embodiment, atank main body 11 formed of a metal, which has a strength to withstandan inner pressure of 10 MPa or more, is filled with a hydrogen storagematerial 12 produced in the Example 1 or 2. The tank main body 11 has aninlet/outlet 13 for loading and unloading hydrogen. The inlet/outlet 13is equipped with a tank valve 14.

[0048] Since the hydrogen storage material 12 of the present inventionis used in the hydrogen storage tank 10, a light-weight hydrogen storagetank 10 capable of storing a large amount of hydrogen can be realized.

[0049] In this embodiment, the hydrogen storage material 12 may beintroduced in the tank main body 11 either as it is or after it has beenappropriately processed into a solid or a thin film form. Furthermore,if necessary, a filter 14A may be provided to prevent leakage of thehydrogen storage material 12 from the tank. The hydrogen storage tank 10may be installed in the fuel cell system or hydrogen engine system of avehicle.

Hydrogen Storage System

[0050] Next, the structure of a hydrogen storage system 20 having thehydrogen storage tank 10 applied thereto will be explained withreference to FIG. 8.

[0051] As shown in FIG. 8, the hydrogen storage system 20 is equippedwith a temperature control apparatus 15 along the periphery of the tankmain body 11 of the hydrogen storage tank 10, for controlling thetemperature of the hydrogen storage tank 10 at a predeterminedtemperature. To the inlet/outlet 13 of the hydrogen storage tank 10, apressure control apparatus 16 is connected. To the pressure controlapparatus 16, a hydrogen suction port 17 and a hydrogen discharge port18 are further connected communicably by way of pipes 19A and 19B,respectively. In the hydrogen storage system 20, hydrogen is suppliedfrom the hydrogen suction port 17 to the tank main body 11 by way of thepressure control apparatus 16 and the tank valve 14, and is stored bythe hydrogen storage material 12. When hydrogen stored in the tank mainbody 11 is taken out, hydrogen is controlled to be guided toward thehydrogen discharge port 18 through the pipe 19B via the tank valve 14and the pressure control apparatus 16.

[0052] By the use of the hydrogen storage material 12 in the hydrogenstorage tank 10 of the present invention, the hydrogen storage system 20storing a large amount of hydrogen can be realized.

Fuel Cell Vehicle

[0053]FIG. 9 shows a fuel cell vehicle 30 having the hydrogen storagesystem 20 installed therein. The fuel cell vehicle 30 includes thehydrogen storage system 20 arranged in the front portion of a vehiclebody 31, a fuel cell stack 21 arranged in the rear portion of thevehicle body 31, and a hydrogen delivering tube 22 connecting thehydrogen storage system 20 and the fuel cell stack 21.

[0054] In the fuel cell vehicle 30 according to the embodiment, sincethe hydrogen storage material 12 charged in the hydrogen storage tank 10has a large hydrogen storage capacity per unit volume or unit weight, itis possible to prevent the entire weight of the hydrogen storage system20 from being increased. Use of the hydrogen storage system 20 of thepresent invention makes it possible to realize the fuel cell vehicle 30capable of storing a sufficient amount of hydrogen to attain along-distance drive.

[0055] The entire content of a Japanese Patent Application No.P2003-039956 with a filing date of Feb. 18, 2003 is herein incorporatedby reference.

[0056] Although the invention has been described above by reference tocertain embodiments of the invention, the invention is not limited tothe embodiments described above will occur to these skilled in the art,in light of the teachings. The scope of the invention is defined withreference to the following claims.

What is claimed is:
 1. A hydrogen storage material, comprising: aplurality of planar molecular layers stacked; and a particle beinginserted into the planar molecular layers to define an interlayerdistance between the planar molecular layers.
 2. The hydrogen storagematerial of claim 1, wherein the particle is at least one of an atom anda molecule.
 3. The hydrogen storage material of claim 1, wherein theparticle is chemically bound to the planar molecular layers.
 4. Thehydrogen storage material of claim 1, wherein the planar molecularlayers are primarily formed of carbon.
 5. The hydrogen storage materialof claim 1, wherein the interlayer distance between the planar molecularlayers, on a condition that hydrogen is stored, is 0.8 to 1.2 nm.
 6. Thehydrogen storage material of claim 1, wherein the particle is analkaline metal atom.
 7. The hydrogen storage material of claim 6,wherein the alkaline metal atom is at least one of potassium, rubidium,and cesium.
 8. The hydrogen storage material of claim 1, wherein aplaner molecule constituting the planar molecular layer contains a metalelement.
 9. The hydrogen storage material of claim 8, wherein the metalelement is at least one of scandium, titanium, vanadium, chromium,manganese, iron, cobalt, nickel, copper, zinc, gallium, aluminium,potassium, rubidium, and cesium.
 10. A method for producing a hydrogenstorage material comprising: arranging a planar molecular layer materialand a metal material at different places in a vacuum chamber, followedby sealing the chamber; and controlling the temperatures of the planarmolecular layer material and the metal material, independently, toinsert a metal atom constituting the metal material between planarmolecular layers constituting the planar molecular layer material. 11.The method for producing a hydrogen storage material of claim 10,wherein a planar molecule constituting the planar molecular layermaterial is primarily formed of carbon.
 12. The method for producing ahydrogen storage material of claim 10, wherein the metal material is analkaline metal.
 13. The method for producing a hydrogen storage materialof claim 12, wherein the alkaline metal is at least one of potassium,rubidium, and cesium.
 14. The method for producing a hydrogen storagematerial of claim 10, wherein a planer molecule constituting the planarmolecular layer material contains a metal element.
 15. The method forproducing a hydrogen storage material of claim 14, wherein the metalelement is at least one of scandium, titanium, vanadium, chromium,manganese, iron, cobalt, nickel, copper, zinc, gallium, aluminium,potassium, rubidium, and cesium.
 16. A hydrogen storage tank,comprising: a hydrogen storage material including a plurality of planarmolecular layers stacked, and a particle being inserted into the planarmolecular layers to define an interlayer distance between the planarmolecular layers.
 17. A hydrogen storage system, comprising: a hydrogenstorage tank including a hydrogen storage material which has a pluralityof planar molecular layers stacked, and a particle being inserted intothe planar molecular layers to define an interlayer distance between theplanar molecular layers.
 18. A fuel cell vehicle, comprising: a hydrogenstorage system comprising a hydrogen storage tank including a hydrogenstorage material which has a plurality of planar molecular layersstacked, and a particle being inserted into the planar molecular layersto define an interlayer distance between the planar molecular layers.